The present invention relates generally to extrusion systems for forming strips of polymeric material and, more particularly, to a preformer for use in such systems to form wide extruded components, such as a rubber tire tread, on a surface of a roller.
Extrusion systems are well known in the art for extruding strips of polymeric material onto a surface of a roller. The extruded component is temporarily carried by the roller and then travels downstream of the roller where it may be further processed into specific rubber tire tread lengths by way of example. Typical extrusion systems include an extruder head which conveys a flow of material through a laterally expanding flow channel to a discharge outlet of the head. Oftentimes, it is necessary to shape the extruded material from the extruder head into a more specific shape before it is extruded through a final profile die onto the surface of the roller.
To this end, roller die preformers are used to shape the flow of material in the interim area between the discharge outlet of the extruder head and the outer circumferential surface of the roller. The preformer is connected in fluid communication with the discharge outlet of the extruder head and is further positioned very close to or even in contact with the roller. The preformer includes a flow inlet configured to receive a flow of material from the discharge outlet of the extruder head and a flow outlet configured to form the extruded component on the surface of the roller.
In the past, roller die preformers have been configured with a flow inlet having a lateral width which is generally equal to the lateral width of the discharge outlet of the extruder head, and further with a flow outlet having a lateral width which is generally narrower than or as wide as the lateral width of the flow inlet. A flow channel is provided within the preformer to convey the flow of material between the flow inlet and the flow outlet so that the extruded component on the surface of the roller may have a lateral width which is narrower than or as wide as the lateral width of the flow inlet depending on the configuration of the preformer. A profile die is mounted to the preformer to profile the extruded material as it exits the flow outlet and is thereafter extruded onto the surface of the roller.
A problem occurs when it is desirable to form an extruded component having a lateral width which is wider than the lateral width of the discharge outlet of the extruder head. In the past, this has required a change to a larger extruder head having an appropriately sized discharge outlet for the desired lateral width of the extruded component. For example, if a thirty-four (34) inch wide extruded component is desired, an extruder head having a discharge outlet with the same or even a wider lateral width has been required. Of course, it will be appreciated that such a change results in a significant expense for the purchase of a wider extrusion head, significant labor and lost production costs associated with installing the wider extruder head, and lost production time as current dies must be redeveloped for the wider extruder head.
Therefore, there is a need for an extrusion system which is capable of forming a variety of extruded component widths on the surface of a roller during an extrusion process while overcoming the drawbacks and shortcomings of extrusion systems heretofore known.
The present invention overcomes the foregoing and other shortcomings and drawbacks of extrusion systems heretofore known for forming wide extruded components on the surface of a roller. While the invention will be described in connection with certain embodiments, it will be understood that the invention is not limited to these embodiments. On the contrary, the invention includes all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention.
In accordance with the principles of the present invention, a roller die preformer is provided for use in an extrusion system to form wide extruded components, such as a rubber tire tread by way of example, on a surface of a roller. The extrusion system includes a conventional extruder head, which conveys polymeric material, including plasticized and elastomeric materials such as rubber, through a laterally expanding flow channel to a discharge outlet of the head.
The roller die preformer of the present invention is connected in fluid communication with the discharge outlet of the extruder head and is further positioned very close to or in contact with a conventional roller so as to form a wide extruded component on a surface of the roller. The preformer has an elongated flow inlet which is configured to receive a flow of material from the discharge outlet of the extruder head and has a lateral width which is generally equal to the lateral width of the discharge outlet of the extruder head. The preformer further includes a laterally expanding flow channel which extends between the flow inlet and an elongated flow outlet of the preformer which has a lateral width which is wider than the lateral width of the flow inlet. The flow channel is configured to laterally expand a flow of material as it travels from the flow inlet to the flow outlet to thereby form a wide extrusion on the surface of the roller.
In accordance with the principles of the present invention, a flow restrictor is configured within the flow channel to urge the flow of material toward the lateral extremities of the flow channel. During an extrusion process, the flow of material impinges on the flow restrictor so that lateral areas of reduced pressure are thereby created on opposite sides of the flow restrictor and toward the lateral extremities of the flow channel. These lateral areas of reduced pressure allow a greater volume of the flow of material to flow toward the lateral extremities of the flow channel and toward the flow outlet as compared to the volume of material flowing proximate the central portion of the flow channel so that a uniform flow distribution across the lateral width of the flow outlet is achieved.
In accordance with the principles of the present invention, the flow of material retains its expanded lateral width as it is extruded onto the outer surface of the roller because the elastic memory of the flow of material has been altered by the lateral expansion of the flow of material within the flow channel as influenced by the configuration of the flow restrictor. In this way, a wide extruded component is formed on the surface of the roller having a lateral width which is wider than the lateral widths of the flow inlet of the preformer and the discharge outlet of the extruder head.
An elongated die plate having an elongated profiled face is mounted to the preformer so as to partially occlude the flow outlet and thereby form a die outlet between the profiled face of the die plate and the outer surface of the roller. The profiled face of the die plate profiles the extrudate as it exits the flow outlet of the preformer and thereafter flows onto the outer surface of the roller to form the wide extruded component in accordance with the principles of the present invention.
The above and other objects and advantages of the present invention shall be made apparent from the accompanying drawings and description thereof.